Method for conformance testing of radio communication equipment

ABSTRACT

The invention provides a method of conformance testing of a secondary station for use in a radio communication system which permits a soft handover process in which the secondary station engages in communication with a plurality of primary stations. The method permits testing the response of the secondary station to power control commands received simultaneously from each of the plurality of primary stations instructing it to adjust its output transmission power. In particular, the method enables testing the secondary station&#39;s assessment of the reliability of the power control commands received from each primary station, which has not been possible previously. 
     The test is performed by transmitting known sequences of power control commands to the secondary station from each of the primary stations, then comparing the actual pattern of changes in output transmission power with the expected pattern of changes.

CROSS REFERENCE TO RELATED APPLICATION

This is a continuation of prior application Ser. No. 09/710,832 filedNov. 13, 2000 now U.S. Pat. No. 6,804,512.

The present invention relates to a method of conformance testing of aradio communication system during soft handover, and to a radio testequipment for carrying out the method. While the present specificationdescribes the method with particular reference to the emerging UniversalMobile Telecommunication System (UMTS), it is to be understood that suchtechniques are equally applicable to use in testing equipment for othermobile radio systems.

There are two basic types of communication required between a BaseStation (BS) and a Mobile Station (MS) in a radio communication system.The first is user traffic, for example speech or packet data. The secondis control information, required to set and monitor various parametersof the transmission channel to enable the BS and MS to exchange therequired user traffic.

In many radio communication systems accurate power control is important.This is particularly so in systems employing spread spectrum CodeDivision Multiple Access (CDMA) techniques, because many communicationchannels share the same bandwidth and so transmission at too high apower in any one channel reduces the signal to noise ratio in all theother channels. Uplink power control, of signals transmitted to a BaseStation (BS) from a Mobile Station (MS), is particularly important. Itensures that the BS receives signals from different MSs at approximatelythe same power level, while minimising the transmission power requiredby each MS. Downlink power control, of signals transmitted by the BS toa MS, is required so that the MS receives signals from the BS with a lowerror rate while minimising transmission power, to reduce interferencewith other cells and radio systems.

In a UMTS embodiment, power control is normally operated in a closedloop manner. For uplink power control the BS determines the requiredchanges in the power of transmissions from a MS and signals thesechanges to the MS by means of Transmit Power Control (TPC) commands. Tominimise overheads, a TPC command typically instructs the MS to increaseor decrease its power, with the change in power being a step ofpredetermined size. However, in some systems a TPC command may alsodetermine the step size to be used.

A MS generally communicates with a single BS. During the course of acall the MS may wish to investigate transferring to another BS, forexample when the quality of the communication link deteriorates as theMS moves away from its BS, or when the relative traffic loading ofdifferent cells requires adjusting. The process of transferring from oneBS to another is known as handover. In a version of this process knownas soft handover, the MS engages in communication with a plurality ofBSs (known as the “active set” of BSs) to determine to which BS, if any,it should transfer. When the MS is engaged in this process, it willreceive TPC commands from each of the BSs at substantially the sametime. It must therefore have an algorithm for determining how to handlea plurality of TPC commands, which may be conflicting.

In one algorithm, which must be supported by a MS suitable for use in aUMTS system, the MS assesses the reliability of the TPC command fromeach BS when deciding how to adjust its transmission power. Methods forperforming this assessment include measuring the Signal-to-InterferenceRatio (SIR) of the received TPC commands, measuring the SIR of othersymbols within the same timeslot (for example pilot symbols), andmeasuring the actual received signal amplitude of the TPC bits beforedecoding, a function of which amplitudes may be known as Soft SymbolInformation (SSI).

To determine whether a MS is suitable for use in a particularcommunication system, such as UMTS, it must undergo conformance tests todetermine whether its operation complies with the relevant standards. Insuch a conformance test to analyse whether a MS is correctly processingTPC commands while performing a soft handover, it is difficult to accessthe result of the MS's estimation of SIR or SSI. Hence it is difficultto assess whether the MS's behaviour is correct.

An object of the present invention is to provide a method of conformancetesting of radio communication equipment during soft handover whichaddresses the above problem. A further object of the present inventionis to enable the required behaviour of radio communication equipmentduring soft handover to be specified.

According to a first aspect of the present invention there is provided amethod for conformance testing of a secondary station for use in a radiocommunication system, the secondary station having means for engaging ina soft handover process in which it communicates with at least twoprimary stations simultaneously and also having power control means foradjusting its output transmission power in response to power controlcommands received from each of the at least two primary stations, themethod comprising operating in a test equipment the steps of:

-   -   generating and transmitting to a secondary station under test at        least two signals equivalent to those transmitted by each of the        at least two primary stations, each signal including a sequence        of power control commands;    -   monitoring the output transmission power of the secondary        station; and    -   determining whether a function of the output transmission power        is within its specified tolerance.

According to a second aspect of the present invention there is provideda radio test equipment for conformance testing of a secondary stationfor use in a radio communication system, the test equipment beingadapted to carry out the test method according to a first aspect of thepresent invention.

By means of the present invention there is provided a method ofconformance testing of a MS processing TPC commands during softhandover.

Embodiments of the present invention will now be described, by way ofexample, with reference to the accompanying drawings, wherein:

FIG. 1 is a block schematic diagram of a radio communication system;

FIG. 2 is a block schematic diagram of a radio communication system witha MS in the process of soft handover; and

FIG. 3 is a flow chart illustrating a method of conformance testing ofradio communication equipment during soft handover in accordance withthe present invention.

In the drawings the same reference numerals have been used to indicatecorresponding features.

Referring to FIG. 1, a radio communication system comprises a primarystation (BS) 100 and a plurality of secondary stations (MS) 110. The BS100 comprises a microcontroller (μC) 102, transceiver means (Tx/Rx) 104connected to antenna means 106, power control means (PC) 107 foraltering the transmitted power level, and connection means 108 forconnection to the PSTN or other suitable network. Each MS 110 comprisesa microcontroller (μC) 112, transceiver means (Tx/Rx) 114 connected toantenna means 116, and power control means (PC) 118 for altering thetransmitted power level. Communication from BS 100 to MS 110 takes placeon a downlink frequency channel 122, while communication from MS 110 toBS 100 takes place on an uplink frequency channel 124.

A MS 110 engaged in a soft handover process is illustrated in FIG. 2,the MS 110 having three two-way communication channels 226 a, 226 b, 226c with three respective BSs 100 a,100 b,100 c. In a given time slot theMS 110 receives substantially simultaneously three TPC commands, onefrom each of BSs 100 a,100 b,100 c. According to one example of a methodof processing these TPC commands, the MS 110 measures the SSI for eachof the three TPC commands, and compares the magnitude of each SSI with apredetermined threshold. If the magnitude if the SSI is above thethreshold the associated TPC command is deemed to be reliable, otherwisethe TPC command is deemed to be unreliable.

One example of a method for combining the TPC commands in the given timeslot is for the MS 110 to reduce its transmitted power if one of the TPCcommands in the time slot is deemed reliable and is interpreted as“down”, or if all of the TPC commands in the time slot are deemedunreliable and are interpreted as “down”. Otherwise the MS 110 willincrease its transmission power.

A method of conformance testing of a MS 110 in accordance with thepresent invention uses n sequences of TPC commands, where n is thenumber of BSs 100 to be used for the soft handover conformance test.FIG. 3 is a flow chart illustrating the steps in such a test performedusing three BSs 100.

The method begins with the generation, at steps 300 a to 300 c, of onesequence of TPC commands for each BS 100 to be used in the soft handoverconformance test (three in this example). The TPC sequences may bedesigned so that any particular set of three simultaneous TPC commands(e.g. 0, 1, 0) will occur a significant number of times, N, during thecourse of the test. For example, a suitable value of N could be about20, in order to provide sufficient samples for a statisticallymeaningful result. It is not necessary for all possible combinations ofTPC commands to be used in such a sequence. As an alternative, a shorterTPC sequence including one or more possible combinations of TPC commandscould be transmitted N times. As a further alternative, the TPCsequences may be pseudo-random.

At steps 302 a to 302 c each BS 100 a,100 b,100 c simultaneouslytransmits its respective sequence of TPC commands, which transmissionspass through respective radio channels 304 a,304 b,304 c which distortthe transmitted signals and add noise. Typically the channels will havepredetermined characteristics and the combined signals will be feddirectly into the antenna input of the MS 110. If the channels do notinclude noise it should be added, preferably as Additive White GaussianNoise (AWGN). This ensures a representative spread of amplitudes for thereceived TPC commands and hence a representative spread of SSI or SIRvalues. The level of noise added should be such that, in combinationwith the channel modeller used, the error rate of received TPC commandsis for example no worse than 10%.

The sequences are received by the MS 110 which, after each triplet ofTPC commands has been received together, processes them, at step 306, todetermine what change in power level should be made. Changes in thetransmission power output of the MS 110 are monitored, at step 308. Whenthe complete sequence of TPC commands has been received a first test isperformed in which the pattern of power changes generated by the MS 110is compared, at step 310 with the expected pattern of power changes. Ifthe pattern is acceptable this aspect of the test is passed, step 312,if not it is failed, step 314.

The acceptability of the actual pattern of power control changes wouldbe judged by determining, for each of the N identical sets oftransmitted TPC commands (or for the complete sequence of sets), theproportion P of these sets for which the MS 110 responds in a particularway. If the value of P is greater than a predetermined value, then itappears that the MS 110 is correctly carrying out the SIR or SSIestimation, and the test is passed. A suitable value for P may depend onthe error rate of the received TPC commands and the number of BSs 100.For the example of a worst-case error rate of 10% and three BSs 100, asuitable value of P could be about 70%.

The acceptable value of P could be set at different levels for differentsets or groups of sets of TPC commands. For example, the probability ofa set of TPC commands being interpreted correctly may be a function ofthe particular commands within the set, which function may depend on themethod used for combining the TPC commands from a set. For example, theproportion P of the sets containing TPC commands [1,1,1] which areinterpreted correctly might take one value P₁, while the proportion ofthe sets [1,1,0], [1,0,1] and [0,1,1] which are interpreted correctlymight take another value P₂, the proportion of the sets [0,0,1], [0,1,0]and [1,0,0] which are interpreted correctly might take a third value P₃and the proportion of the sets [0,0,0] which are interpreted correctlymight take a fourth value P₄.

A further test may be performed in addition to or instead of the firsttest. When the complete sequence of TPC commands has been received thistest determines, at step 316, the final output power of the MS 110. Thispower is tested, at step 318, to see if it is within a predeterminedrange relative to the output power at the start of the test. If it isthen this aspect of the test is passed, step 320, if not it is failed,step 322.

As an example of how an acceptable range of powers may be determined,consider the case where n_(u) sets of TPC commands are transmitted, eachof which sets should be interpreted as “up” after the MS 110 hasperformed its combination process. For example, with a worst-case errorrate of received TPC commands from each BS 100 a,100 b,100 c of 5%, atleast 85% of the sets of commands should be interpreted correctly by theMS 110. Hence, the expected power change from these sets of TPC commandsis (0.85±0.15)n_(u)(Δ_(TPC)±δ_(Δ)), where Δ_(TPC) is the power controlstep size used by the MS 110 and δ_(Δ) is the tolerance in the powercontrol step size (assessed by a separate test). Similarly, if n_(d)sets of TPC commands are transmitted, each of which sets should beinterpreted as “down” after the combination process, the expected powerchange is −(0.85±0.15)n_(d)(Δ_(TPC)±δ_(Δ)). Hence, the total expectedpower change by the end of the test is(0.85±0.15)(n _(u) −n _(d))(Δ_(TPC)±δ_(Δ))This latter test is most likely to be useful where there is a low TPCerror rate, a small number of BSs 100 and a significant differencebetween the values of n_(u) and n_(d). These conditions will result inthe total expected power change being a significant number of step sizesand having a relatively small expected tolerance.

In the description above a plurality of BSs 100 were used generate andtransmit signals to the MS 110. However, in a practical test system suchsignals could equally well be generated by a Radio Frequency (RF) signalgenerator forming part of the test system.

The present invention has been described in relation to the testing of aMS suitable for use in a UMTS embodiment. However, it is generallyapplicable to any system employing closed loop power control wherecommands are received from multiple base stations simultaneously and theresulting action may be dependent on properties of the commands whichare untestable because they are determined internally by the equipmentunder test.

From reading the present disclosure, other modifications will beapparent to persons skilled in the art. Such modifications may involveother features which are already known in methods of conformance testingof radio communication equipment, and which may be used instead of or inaddition to features already described herein. Although claims have beenformulated in this application to particular combinations of features,it should be understood that the scope of the disclosure of the presentapplication also includes any novel feature or any novel combination offeatures disclosed herein either explicitly or implicitly or anygeneralisation thereof, whether or not it relates to the same inventionas presently claimed in any claim and whether or not it mitigates any orall of the same technical problems as does the present invention. Theapplicants hereby give notice that new claims may be formulated to suchfeatures and/or combinations of features during the prosecution of thepresent application or of any further application derived therefrom.

In the present specification and claims the word “a” or “an” precedingan element does not exclude the presence of a plurality of suchelements. Further, the word “comprising” does not exclude the presenceof other elements or steps than those listed.

1. A test method for conformance testing of a secondary station engagingin a soft handover testing process in which the secondary stationcommunicates with a primary station whereby an output transmission powerof the secondary station is adjustable in response to power controlcommands received by the secondary station from the primary station, thetest method comprising: receiving a one or more test signals from theprimary station, each test signal including a sequence of powercommands, wherein each sequence of power commands in the one or moretest signals is arranged to establish a particular combination of powercontrol commands that occurs a plurality of times during the receptionof the plurality of test signals by the secondary station; adjusting andmonitoring the output transmission power of the secondary station basedon the one or more test signals received from the primary station; anddetermining whether a function of the output transmission power of thesecondary station is within a specified tolerance associated with thesecondary station.
 2. The test method of claim 1, wherein the functionof the output transmission power is a sequence of changes of the outputtransmission power based on the one or more test signals received fromthe primary station.
 3. The test method of claim 1, wherein thespecified tolerance is a function the one or more test signals receivedfrom the primary station.
 4. The test method of claim 1, wherein thefunction of the output transmission power is a difference between afirst level of the output transmission power prior to receiving the oneor more test signals received from the primary station and a secondlevel of the output transmission power subsequent to adjusting andmonitoring the output transmission power of the secondary station basedon the one or more test signals received from the primary station. 5.The test method of claim 1, wherein the secondary station uses anestimate of a reliability of the one or more test signals received fromthe primary station in determining a required change in the outputtransmission power.
 6. The test method of claim 1, wherein the sequenceof power control commands in each test signal is pseudo-random.
 7. Thetest method of claim 1, wherein each sequence of power control commandsis arranged to establish a sub-sequence of power control commands thatoccurs a one or more times during the reception of the one or more oftest signals by the secondary station.
 8. The test method of claim 1,wherein the secondary station simultaneously receives the one or moretest signals from the primary station.
 9. A secondary station engagingin a soft handover test process in which the secondary stationcommunicates with a primary station whereby an output transmission powerof the secondary station is adjustable in response to power controlcommands received by the secondary station from the primary station, thesecondary station comprising: a transceiver capable of receiving one ormore test signals from the primary station, each test signal including asequence of power commands, wherein the sequences of power commands atleast establish a particular combination of power control commands,which combination occurs one or more times during the reception of theone or more test signals by the secondary station; a power controller inelectrical communication with the transceiver, wherein the powercontroller is operable to adjust the output transmission power based onthe one or more test signals received from the primary station; and amicrocontroller in electrical communication with the transceiver and thepower controller, wherein the microcontroller is operable to monitor anadjustment of the output transmission power by the power controllerbased on the one or more test signals received from the primary station,and wherein the microcontroller is further operable to determine whethera function of the output transmission power is within a specifiedtolerance associated with the secondary station.
 10. The secondarystation of claim 9, wherein the function of the output transmissionpower is a sequence of changes of the output transmission power based onthe one or more test signals received from the primary station.
 11. Thesecondary station of claim 9, wherein the specified tolerance is afunction of the one or more test signals received from the primarystation.
 12. The secondary station of claim 9, wherein the function ofthe output transmission power is a difference between a first level ofthe output transmission power prior to receiving the one or more of testsignals from the primary station and a second level of the outputtransmission power subsequent to adjusting and monitoring the outputtransmission power of the secondary station based on the one or moretest signals received from the primary station.
 13. The secondarystation of claim 9, wherein the microcontroller uses an estimate of areliability the one or more test signals received from the primarystation in determining a required change in the output transmissionpower.
 14. The secondary station of claim 9, wherein the sequence ofpower control commands in each test signal is pseudo-random.
 15. Thesecondary station of claim 9, wherein the particular combination ofpower control commands is a sub-sequence of power control commands. 16.The secondary station of claim 9, wherein the transceiver simultaneouslyreceives the one or more test signals from the primary station.
 17. Asecondary station engaging in a soft handover test process in which thesecondary station communicates with a primary station whereby an outputtransmission power of the secondary station is adjustable in response topower control commands received by the secondary station from theprimary station, the secondary station comprising: means for receiving aone or more test signals from the primary station, each test signalincluding a sequence of power commands; means for adjusting andmonitoring the output transmission power of the secondary station basedon the one or more test signals received from the primary station; andmeans for determining whether a function of the output transmissionpower of the secondary station is within a specified toleranceassociated with the secondary station.